Enterprises commonly maintain multiple copies of important data and expend large amounts of time and money to protect this data against losses due to disasters or catastrophes. One class of techniques for maintaining redundant data copies is known as mirroring, in which copies of data are located at both a primary storage location and a secondary or remote storage location. If the data is mirrored to an offsite location, then the data is protected against disasters and catastrophes, such as fire, power outages, theft, earthquakes, tornadoes, hurricanes, floods, etc. Many data processing systems employ multiple levels of redundancy to protect data and locate these systems at separate geographical locations.
Data processing systems often utilize disk mirroring to replicate data onto separate logical disk volumes using one of various techniques, such as synchronous mirroring or asynchronous mirroring. Synchronous mirroring is generally used when response distances between copy storage are short and data cannot be lost. By contrast, asynchronous mirroring is used when the smallest possible performance impact is to be imposed on the primary site and mirrored data is to travel long distances. Asynchronous mirroring is often used for very large geographical scale operations.
Due to proprietary protocol requirements, storage arrays coupled to replicate data are homogenous. Companies spend thousands or even millions of dollars to purchase matching pairs of arrays that perform disaster recovery failover and failback.